1) Field of the Invention
The present invention relates to a rotating angle measuring device and method for a rotary object and, more particularly, to a rotating angle measuring device and method for a rotary object by which a rotating angle of a rotary object can be measured accurately and an error in the rotating angle can be compensated for.
2) Description of Related Art
Generally, an autocollimator 1 and a polygon mirror base 2 are used for measuring an accuracy of a rotating angle, which will be described hereinafter with reference to FIG. 1.
As shown in FIG. 1, a plurality of reflecting mirrors 3 are formed symmetrically on the outer circumference of the polygon mirror base 2. Normals l, lxe2x80x2 of the reflecting mirrors 3 which are adjacent to each other meet at a rotating center R of the polygon mirror base 2 at a predetermined division angle xcex1.
Such a polygon mirror base 2 is disposed on a rotary object like a link of a robot, etc., a rotating angle of which should be measured accurately. In this case, the rotating center R of the polygon mirror base 2 should be located in alignment with a rotating axis of the link of the robot. The autocollimator 1 emits a measuring beam to the reflecting mirror 3 and receives the beam reflected from the mirror 3, thereby displaying a horizontal angle of the autocollimator 1 on a displaying part (not shown).
In an initial condition, the autocollimator 1 is mounted perpendicularly to the reflecting mirror 3 of the polygon mirror base 2 so that the horizontal angle of the autocollimator 1 is set to 0xc2x0. Then, the link of the robot is rotated several times by the division angle xcex1 of the polygon mirror base 2, and the autocollimator 1 emits the measuring beam to the reflecting mirror 3 at every rotation of the link so as to measure the horizontal angle of the autocollimator 1, thereby detecting whether the link rotates accurately by the division angle xcex1 of the polygon mirror base 2.
That is, if the link of the robot rotates precisely by the division angle xcex1 of the polygon mirror base 2, the horizontal angle of the autocollimator 1 is continuously measured at 0xc2x0. If not, the horizontal angle of the autocollimator 1 shows numerically the error of the rotating angle of the link.
By using the above method, an error of a rotating angle of a rotary object like a link of a robot, etc. can be measured and compensated so as to improve an operation accuracy of the rotary object.
However, in the conventional rotating angle measuring device comprising the autocollimator 1 and polygon mirror base 2 as described above, since the polygon mirror base 2 is producible only to the minimum division angle xcex1 of 5xc2x0 due to the manufacturing limits of accuracy, etc., it is impossible that the conventional measuring device is applied to rotary objects which are used in high-precision works requiring a rotating angle under 5xc2x0.
Furthermore, in mounting the polygon mirror base 2 to the rotary object to be measured, it is so difficult to locate the rotating center R of the polygon mirror base 2 precisely in alignment with the rotating axis of the rotary object.
The present invention has been made in an effort to solve the above problems.
It is an objective of the present invention to provide a rotating angle measuring device and method for a rotary object by which a minute rotating angle of a rotary object can be measured accurately and an error of rotation is compensated for so that the rotary object can be applied to high-precision works.
To achieve the above objective, the present invention provides a rotating angle measuring device for measuring a rotating angle of a rotary object comprising: a holder mounted detachably to the rotary object so that the holder is rotated together with the rotary object; a rotating angle sensor coupled to the holder and having a shaft which is rotated relative to the holder; a level coupled to the shaft of the rotating angle sensor which provides an initial value as a datum for operation of the rotating angle sensor at an initial position of the rotary object; and an operation part which rotates the shaft of the rotating angle sensor. After rotation of the rotary object from the initial position to a second position, a rotating angle of the shaft is measured with the rotating angle sensor by rotating the shaft using the operation part until the changed value of the level caused by the rotation of the rotary object is returned to the initial value, thereby determining a rotating angle of the rotary object.
The holder preferably comprises a mounting plate which is attached to the rotary object, a supporting plate to which the rotating angle sensor is fixed, and a plurality of connecting bars which connect the supporting plate to the mounting plate.
The operation part preferably includes a worm which is provided to the holder, and a worm wheel which is toothed with the worm and which is coupled to the shaft of the rotating angle sensor so as to be rotated together with the shaft by rotation of the worm, the shaft passing through the center portion of the worm wheel.
A rotating plate, through which the shaft of the rotating angle sensor is passed, is attached to the worm wheel so as to be rotated together with the shaft by the driving of the worm and the worm wheel. The level is also mounted fixedly to the rotating plate.
A driving plate for rotating the worm and a knob protruded from a surface of the driving plate are provided to one end of the worm.
Preferably, the rotating angle sensor is a rotary encoder.
Also, the present invention provides a rotating angle measuring method for a rotary object comprising the steps of: mounting a rotating angle sensor and a level to the rotary object, with the level being coupled to a shaft of the rotating angle sensor and rotated together with the shaft; setting an initial value of the level at an initial position of the rotary object; rotating the rotary object at a target rotating angle from the initial position to a second position; returning the changed value of the level due to the rotating step to the initial value by rotating the level; and measuring a practical rotating angle of the rotary object from the initial to the second position by measuring with the rotating angle sensor the rotating angle of the shaft which is rotated together with the level during the returning step.
The rotating angle measuring method further comprises a compensating step after the measuring step, in which the practical rotating angle of the rotary object measured in the measuring step is analyzed and a deviation between the target rotating angle and the practical rotating angle is calculated and compensated for.